Research ArticleFlexural Properties and Elastic Modulus of Different EstheticRestorative Materials: Evaluation after Exposure to Acidic Drink

Andrea Scribante ,1 Marco Bollardi,2 Marco Chiesa,2

Claudio Poggio ,2 andMarco Colombo2

1Unit of Orthodontics and Paediatric Dentistry, Section of Dentistry, Department of Clinical, Surgical,Diagnostic and Paediatric Sciences, University of Pavia, Pavia, Italy2Unit of Restorative Dentistry, Section of Dentistry, Department of Clinical, Surgical, Diagnostic and Paediatric Sciences,University of Pavia, Pavia, Italy

Correspondence should be addressed to Andrea Scribante; andrea.scribante@unipv.it

Received 25 September 2018; Revised 11 January 2019; Accepted 27 January 2019; Published 4 February 2019

Academic Editor: Devanand P. Fulzele

Copyright © 2019 Andrea Scribante et al. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.

Background. Acidic beverages, such as soft drinks, can produce erosion of resin composites.The purpose of the present study was toinvestigate mechanical properties of different esthetic restorative materials after exposure to acidic drink. Methods. Nine differentcomposites were tested: nanofilled (Filtek Supreme XTE, 3M ESPE), microfilled hybrid (G-ænial, GC Corporation), nanohybridOrmocer (Admira Fusion, Voco), microfilled (Gradia Direct, GC Corporation), microfilled hybrid (Essentia, GC Corporation),nanoceramic (Ceram.XUniversal, DentsplyDeTrey), supranano spherical hybrid (EsteliteAsteria, TokuyamaDental Corporation),flowablemicrofilled hybrid (Gradia Direct Flo, GCCorporation), and bulk fill flowable (SureFil SDR flow,DentsplyDe Trey).Thirtyspecimens of each esthetic restorativematerial were divided into 3 subgroups (n=10): specimens of subgroup 1 were used as control,specimens of subgroup 2 were immersed in 50ml of Coca Cola for 1 week, and specimens of subgroup 3 were immersed in 50ml ofCoca Cola for 1 month. Flexural strength and elastic modulus were measured for each material with an Instron Universal TestingMachine. Data were submitted to statistical analysis. Results. After distilled water immersion, nanofilled composite showed thehighest value of both flexural strength and elastic modulus, but its flexural values decreased after acidic drink immersion. Nosignificant differences were reported between distilled water and acidic drink immersion for all other materials tested both forflexural and for elastic modulus values. Conclusions. Even if nanofilled composite showed highest results, acidic drink immersionsignificantly reduced flexural values.

1. Introduction

Dental caries is an infective process that causes the fade ofthe tooth’s hydroxyapatite. This process is mainly due to aciddegradation of tooth structures. In order to stop the progres-sion of this disease, the infected tissue has to be removedand it has to be replaced with a filling material [1]. In thepast, amalgam was used to replace the infected material, butnowadays dental composites are used to fill the cavity. Unlikeamalgam, composites are more difficult to place and they arecorroded more easily by the acids of the oral cavity [2–4].

Composites are also used to treat other noncarious lesionsof dental tissues, such as in case of dental erosion. This

process is an irreversible loss of dental hard tissue by achemical processwithout the involvement ofmicroorganismsand this is due to either extrinsic (e.g., high consumption ofacid beverages and other acid substances) or intrinsic (e.g.,recurrent vomiting due to anorexia and bulimia) sources[5, 6]. In fact, many studies demonstrated that the acidscontained in beverages [for example, coca cola] cause theerosion of the enamel, both in vitro and in vivo [7–9].These acid substances can damage the tissues of the teeth,but also the materials used to restore the teeth [10]. Infact, it is demonstrated that the persistence of the com-posites into an acidic environment can cause a loss ofmechanical properties of composites, glass-ionomer cements,

HindawiBioMed Research InternationalVolume 2019, Article ID 5109481, 8 pageshttps://doi.org/10.1155/2019/5109481

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Figure 1: Ad hoc stainless-steel device for specimen preparation.

and polyacid modified composites [11, 12]. The creation ofmicroinfiltration between the enamel and the restaurationhas been reported [13]. Moreover, acidic environment makesthe surface of the composites rougher [14].Many studies eval-uated mechanical properties of composites [15, 16]. However,there are no studies about the change of flexural strength andelastic modulus of composite resins after exposure to acidicdrinks.

The purpose of the present investigation was to evaluateand compare deflection strengths and elastic modulus ofvarious composites tested after acidic drink immersion.

2. Methods

2.1. Specimen Preparation. The 9 different composites weredivided into groups (Table 1): (1) nanofilled composite (FiltekSupreme XTE, 3M ESPE, St. Paul, Minnesota, USA), (2)microfilled hybrid composite (G-ænial, GC Corporation,Tokyo, Japan), (3) nanohybrid Ormocer based composite(Admira Fusion, Voco, Cuxhaven, Germany), (4) microfilledcomposite (Gradia Direct, GC Corporation, Tokyo, Japan),(5) microfilled hybrid composite (Essentia, GC Corporation,Tokyo, Japan), (6) nanoceramic composite (Ceram.XUniver-sal, Dentsply De Trey, Konstanz, Germany), (7) suprananospherical hybrid composite (Estelite Asteria, TokuyamaDental corporation, Taitou-kuTokyo, Japan), (8) microfilledhybrid flowable composite (Gradia Direct Flo, GC Corpo-ration, Tokyo, Japan), and (9) bulk composite (SureFil SDRflow, Dentsply De Trey, Konstanz, Germany).

Thirty rectangular prism-shaped specimens (2mm ×2mm× 25mm) of each composite were prepared [17] with adhoc stainless-steel device (Figure 1). The surface-to-volumeratio was 2,08mm−1. Once the composite was packed intothe device, a mylar strip was used to make a flat surface ofthe specimen. Then all the specimens were light-cured for 3minutes [18] into a light polymerization oven (Spectramat,Ivoclar Vivadent AG, Schaan, Liechtenstein light intensity:1200mW/cm2, Wavelength: 430-480 nm, Lamp socket: R7s,Lamp Diameter: 13.5mm, Lamp length: 160mm). Afterpolymerization, the specimens were stored in distilled waterat 37∘C and 100% humidity before performing the flexuralstrength test.

Figure 2: Testing apparatus, before test.

2.2. Immersion in Acidic Drink. Each group of composites(total size for each group: 30 specimens) was divided intothree subgroups (A, B, and C) of ten specimens each: thefirst subgroup (A) was used as control and were testedimmediately after storage in distilled water for 24 hours;the specimens of the second subgroup (B) were immersedin 50ml of acidic drink (Coca Cola/Coca Cola Company,Atlanta, Georgia, United States) for 1 week; the specimensof the last subgroup (C) were immersed in 50ml of acidicdrink (Coca Cola/Coca Cola Company, Atlanta, Georgia,United States) for 1 month. All specimens were immersedat 37∘C and 100% humidity environment. A single specimenhas been immersed for each of the 50ml aliquots. The acidicdrink was changed once a week for all the time [19]. ThepH of acidic storage solution has been measured beforespecimen immersion (pH=2.4). For subgroup B another pHmeasurement has been performed before specimen testing(pH=2.4). On the other hand, for subgroup C pH valueswere recorded each week after solution change (pH=2.4) andbefore testing (pH=2.4).

2.3. Mechanical Test. Each sample was placed in an appro-priate aluminum framework (Figure 2). The span lengthbetween supports was 21mm and the crosshead speed wasset at 1mm per minute [20]. The compressive load wasappliedwith a universal testingmachine (Model 3343, InstronCorporation, Canton, MA, USA) to the middle of the testspecimens [21].

After specimen failure (Figure 3) the flexural strength val-ues were recorded with computer software (Bluehill, InstronCorporation, Canton, Ma, USA).

After collecting the data, the flexural strength (𝜎) and theelastic modulus (E) have been calculated [22].

Statistical analysis was performed with computer soft-ware (R version 3.1.3, R Development Core Team, R Foun-dation for Statistical Computing, Wien, Austria). Descrip-tive statistics were calculated (mean and standard deviationvalues). Normality of the distributions was assessed withKolmogorov and Smirnov test. Nonparametric analysis ofvariance (Kruskal-Wallis) was applied to determine whether

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Table 1: Materials tested in the present study.

Material Type Composition Filler Content %(w/w) Manufacturer Lot #

Filtek SupremeXTE Nanofilled composite

Matrix: Bis-phenol Adiglycidylmethacrylate (Bis-GMA),triehtylene glycol dimethacrylate

(TEGDMA), urethane dimethacrylate(UDMA), bis-phenol A polyethylene

glycol diether dimethacrylateFiller: silica nanofillers (5-75 nm),

zirconia/silica nanoclusters (0.6-1.4 𝜇m)

78.5 (w/w) 3M ESPE, St Paul,MN, USA N748173

G-aenial Microfilled hybridcomposite

Matrix: urethane dimethacrylate(UDMA), dimethacrylate

co-monomers.Filler: silica, strontium, lanthanoidfluoride (16-17 𝜇m), silica (>100 nm)

fumed silica (<100 nm)

76 w/w GC Corporation,Tokyo, Japan 151029A

Admira Fusion Nanohybrid Ormocerbased composite

Matrix: resine OrmocerFiller: silicon oxide nano filler, glass

ceramics filler (1 𝜇m)84 (w/w) Voco, Cuxhaven,

Germany 1601121

Gradia Direct Microfilled composite

Matrix: urethanedimethacrylate(UDMA), dymethacrylate

camphorquinoneFiller: fluoro-alumino-silicate glass

silica powder

73 (w/w) GC Corporation,Tokyo, Japan 150527A

Essentia Microfilled hybridcomposite

Matrix: urethane dimethacrylate(UDMA), Bis-MEPP, Bis-EMA,

Bis-GMA, TEGDMAFiller: prepolymerised fillers, barium

glass, fumed silica

81 w/w GC Corporation,Tokyo, Japan 151109C

Ceram.X Universal Nanoceramiccomposite

Matrix: methacrylate modifiedpolysiloxane, dimethacrylate resin,fluorescent pigment, UV stabilizer,stabilizer, camphorquinone, ethyl-4

(dimethylamino) benzoate, iron oxidepigments, aluminium sulfo silicate

pigments.Filler: Barium-aluminium borosilicate

glass (1.1-1.5 𝜇m), Methacrylatefunctionalized silicon dioxide nanofiller

(10 nm)

76 (w/w) Dentsply De Trey,Konstanz, Germany 1507000661

Estelite Asteria Supra-nano sphericalhybrid composite

Matrix: Bis-phenol Adiglycidylmethacrylate (Bis-GMA),

Bisphenol A polyethoxymethacrylate (Bis-MPEPP), triehtyleneglycol dimethacrylate (TEGDMA),urethane dimethacrylate (UDMA)Filler: Supra-nano Spherical filler(200nm spherical SiO2-ZrO2),Composite Filler (include 200nm

spherical SiO2-ZrO2).

82 (w/w)

Tokuyama Dentalcorporation,

Taitou-kuTokyo,Japan

6,6E+17

Gradia Direct Flo Flowable Microfilledhybrid composite

Matrix: Modified UDMA, EBPADMA,TEGDMA

Filler: Ba–Al–F–B–Si–glass,St–Al–F–Si–glass 68 wt%, 44 vol%

GC Corporation,Tokyo, Japan 160602A

SureFil SDR flow Bulk Fill Flowable

Matrix: Modified UDMA, EBPADMA,TEGDMAFiller:

Barium-alumino-fluoro-borosilicateglass, strontium alumino-fluoro-silicate

glass 47,3 vol%

Dentsply De Trey,Konstanz, Germany 1703001234

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Table 2: Mean values (and standard deviations) of flexural strength (MPa). Values have been collected after storage in physiologic solution(Subgroup A, t0), after one week (Subgroup B, t1), and after 30 days (Subgroup C, t2) of immersions in acidic drink.

Group 1 (FiltekSupreme XTE)

Group 2(G-ænial)

Group 3(AdmiraFusion)

Group 4(GradiaDirect)

Group 5(Essentia)

Group 6(Ceram.XUniversal)

Group 7(EsteliteAsteria)

Group 8(Gradia

Direct Flo)

Group 9(SureFilSDR flow)

Subgroup A(t0) 148,58 (17,77) 92,31

(9,85)58,88(13,54)

90,21(21,27)

103,22(16,90) 91,67 (21,69) 80,29

(7,58) 112,27 (2,31) 105,16 (4,08)

Subgroup B(t1) 93,07 (22,84) 70,94

(19,55)60,66(6,81)

82,98(14,94)

81,14(19,24) 96,93 (10,56) 70,11 (1,11) 101,61 (16,18) 94,57 (6,64)

Subgroup C(t2) 82,98 (24,26) 64,86

(10,90)60,07(17,78)

83,55(12,41)

71,52(12,50) 111,14 (4,84) 69,23

(2,39) 118,40 (3,77) 99,89 (5,98)

Figure 3: Testing apparatus, after test.

there were significant differences among the various groups.Mann–Whitney post hoc test was applied. Significance for allstatistical tests was predetermined at P<0.05.

3. Results

3.1. Flexural Strength. Mean and standard deviations ofthe various groups are illustrated in Table 2 and Figure 4.Kruskal-Wallis showed significant differences among groups(P<0.0001). Post hoc test showed that, after 24 hours’ immer-sion in distilled water (Subgroup A), Filtek Supreme XTE(Group 1) has revealed the highest value of flexural strengthif compared with all the composites tested (P<0.05). AdmiraFusion (Group 3) recorded the lowest flexural strength values,but the difference was significant only with Essentia (Group5), Gradia Direct Flo (Group 8), and SureFil SDR flow(Group 9) (P<0.05). The results of the groups that shovedintermediate flexural strength values were as follows: G-ænial(Group 2), Gradia Direct (Group 4), Essentia (Group 5),Ceram.X Universal (Group 6), Estelite Asteria (Group 7),Gradia Direct Flo (Group 8), and SureFil SDR flow (Group 9)showed similar values of flexural strength and no significantdifference has been reported among them (P>0.05).

When evaluating the samples of Subgroups B (after 1-week Coca Cola immersion) and C (after 1-month CocaCola immersion), Filtek Supreme XTE showed a significant

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Figure 4: Flexural strength (MPa) for each material tested after 24hours’ distilled water storage (SubgroupA, blue columns), one-weekacidic drink storage (Subgroup B, orange columns), and 30 days’acidic drink storage (Subgroup C, grey columns).

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Distilled waterCoca Cola 1 weekCoca Cola 1 month

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Figure 5: Elastic Modulus (MPa) for each material tested after 24hours’ distilled water storage (SubgroupA, blue columns), one-weekacidic drink storage (Subgroup B, orange columns), and 30 days’acidic drink storage (Subgroup C, grey columns).

decrease in flexural strength if compared with distilled waterimmersion (Subgroup A) (P<0.05). All the other compositestested showed no significant differences in flexural strengthvalues among the three different storage conditions (P>0.05),except for Filtek Supreme XTE (Group 1) that showedsignificantly higher values after storage in distilled water thanafter 30 days of acidic drink storage (P<0.05).

3.2. Elastic Modulus. Mean and standard deviations of thevarious groups are illustrated in Table 3 and Figure 5.Kruskal-Wallis showed significant differences among groups

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Table 3: Mean values (and standard deviations) of elastic modulus (GPa). Values have been collected after storage in physiologic solution(Subgroup A, t0), after one week (Subgroup B, t1) and after one month (Subgroup C, t2) of immersions in acidic drink.

Group 1 (FiltekSupreme XTE)

Group 2(G-ænial)

Group 3(AdmiraFusion)

Group 4(GradiaDirect)

Group 5(Essentia)

Group 6(Ceram.XUniversal)

Group 7(EsteliteAsteria)

Group 8(Gradia

Direct Flo)

Group 9(SureFilSDR flow)

Subgroup A(t0) 9,45 (0,78) 5,25 (0,35) 5,06

(0,59) 4,11 (0,38) 6,27 (0,57) 7,12 (1,12) 6,57(0,68) 3,05 (0,60) 3,40 (0,23)

Subgroup B(t1) 7,83 (1,47) 4,65 (0,19) 5,52 (0,43) 3,90 (0,59) 5,70 (0,05) 6,81 (0,19) 5,45 (0,33) 3,50 (0,15) 3,22 (0,34)

Subgroup C(t2) 7,16 (0,89) 4,68

(0,37) 5,23 (0,15) 4,00 (0,33) 5,60(0,49) 6,92 (0,20) 5,65 (0,69) 3,60 (0,04) 3,49 (0,47)

(P<0.0001). Post hoc test showed that, after 24 hours’ immer-sion in distilled water (Subgroup A), Filtek Supreme XTE(Group 1) showed the highest value of elastic modulus incomparison of all the other composites (P<0.05). Ceram.XUniversal (Group 6) showed no significant differences in elas-tic modulus values if compared with Essentia (Group 5) andEstelite Asteria (Group 7). The lowest values were recordedwith Gradia Direct (Group 4), Gradia Direct Flo (Group 8),and SureFil SDR flow (Group 9), which showed no significantdifference among them (P>0.05). Gradia Direct (Group 4)showed no significant differences in elastic modulus alsoif compared with G-Aenial (Group 2) and Admira Fusion(Group 3) (P>0.05).

When evaluating the samples of Subgroups B (after 1-week Coca Cola immersion) and C (after 1-month CocaCola immersion) similar results were reported, except forFiltek Supreme XTE (Group 1) that showed no significantdifferences (P>0.05) with Ceram.X Universal (Group 6).

Each of the composites tested showed no significant dif-ferences in elastic modulus values among the three differentstorage conditions (P>0.05), except for Filtek Supreme XTE(Group 1) that showed significantly higher values after storagein distilled water than after both one week and 30 days ofacidic drink storage (P<0.05).

4. Discussion

Durability of restorations in the oral cavity is highly affectedby the resistance to dissolution or disintegration caused byfoods, drinks, and the acidity produced by bacteria [23].Postprandial pH usually becomes more acid as it falls tovalues below 4. Moreover, many beverages, like Coca Cola,have a value of pH lower than 4. Many scientific studieshave shown that enamel dissolution occurs below pH 4 andoccurs for the dental composites [5]. Fillers of compositeresins have been reported to fall out from resin materialsand the matrix component decomposes when exposed to lowpHenvironments [10]. Furthermore, resin-based restorationsundergo greater micromorphological damage when remain-ing in an acidic environment for a long time [14]. In thepresent study the effect of low pH environment on differentdental composites has been evaluated after both one weekand 30 days of storage and compared with a control groupstored in distilled water for 24 hours. Immersion in distilledwater has not been performed after 30 days. In fact, the

immersion in water for short term storage periods (withinone month) has been demonstrated to have minimal ornegligible effect on flexural properties and elastic modulusof composite materials [15]. Moreover, the decrease overtime of flexural strength of composite resins stored in waterseems to be related more to cyclical fatigue than to storagesolution [16]. Our report simulated the acidic environmentof the oral cavity by an uninterrupted immersion of thespecimens in Coca Cola. However, a limitation of this invitro model is that other factors have not been considered,such as salivary buffering capacity and acquired pellicle [10].However, the simulated immersion in acidic drinks has beendemonstrated to be a valuable in vitro simulation conditionto test composite dental materials [23–25].

In the present report, the flexural strength and elasticmodulus of different composite materials have been tested.Previous studies evaluated flexural strength and elastic mod-ulus of various dental materials. Many reports have been pre-sented about fiber-reinforced composites used as endodonticposts [26], nets [27], and long fibers [21].Thesematerials havebeen proposed for endodontic [28], prosthodontic [29], andsplinting purposes [30]. However, only few reports evaluatedflexural strength of nonfiber reinforced dental materials.Only the relationship between flexural strength and thepostcuring treatment [17] and the relationship between flex-ural strength and the different polishing protocols [31] havebeen tested nowadays. No studies evaluated flexural strengthand acidic aging.

The persistence of an acidic environment can cause aloss of mechanical properties of composites, glass-ionomercements, and polyacid modified composites [11, 12]. In fact,in the present report, the acidic beverage affected only a littlethe flexural strength of the various composites tested. This isprobably due to the different chemistry of the materials tested(composites in the present investigations and compomersor glass ionomer cements in previous reports). In fact,compomers and glass ionomers have the ability to bufferexternal storagemedia [11], and this could explain their majorsusceptibility to acid attack.

In the present report, the most affected composite is thenanofilled composite (Filtek supremeXTE,Group 1), which isalso the composite that has reached the highest value of flexu-ral strength under physiologic solution storage. Furthermore,value of flexural strength of nanofilled composite (Group 1)after onemonth of Coca-Cola reached the average value of all

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the other composites. Regarding other composites, the effectof the acidic beverage does not affect significantly the flexuralstrength. Therefore, nanofilled composites present higherflexural strength than all other materials tested withoutimmersion in acidic drink solution. On the other hand, inacidic environment no difference was reported among allmaterials tested.

It is also possible to notice that Admira Fusion (Group 3)has the lowest value of flexural strength. This is a nanohybridOrmocer based composite, and it is a different type ofcomposite compared to all of the other composites tested.Ormocer is a composite technology that literally meansORganically MOdified CERamics [32]. These materials aremade of inorganic-organic hybrid polymers that form asiloxane network modified by the incorporation of organicgroups. This type of composite shows, as a positive aspect,a lower cytotoxic effect than conventional dimethacrylate-based composites [33]. On the other hand, the first generationof ormocers have showed poorer long-term clinical behaviorthan conventional composites [34].This is in agreement withthe findings of the present report, as the nanohybridOrmocerbased composite (Admira Fusion, Group 3) presented thelowest value of flexural strength compared to other compos-ites tested.

Flexural strength is a clinically relevant property forrestorative materials, as it simulates composite use in high-stress bearing areas [35, 36]. Moreover, there is an ISO4049/2009, which put the limit of 80MPa for polymer-based restorative materials claimed by the manufactureras suitable for restorations involving occlusal surfaces [37].In the present report, under physiologic solution storage,the only material that is not above this ideal value is thenanohybrid Ormocer composite (Group 3). On the otherhand, after 1-week acidic drink storage, also microfilledhybrid composite (G-ænial, Group 2) and supranano spher-ical hybrid composite (Estelite Asteria, Group 7) presentedflexural strength values under this limit. After 1 month alsomicrofilled hybrid composite (Essentia, Group 5) decreasedits strength performances under 80MPa. Other materials,such as nanofilled composite (Filtek Supreme XTE, Group1), microfilled composite (Gradia Direct, Group 4), nanoce-ramic composite (Ceram.X Universal, Group 6), microfilledhybrid composite (Gradia Direct Flo, Group 8), and bulk fillflowable (SureFil SDR Flow, Group 9), lowered their flexuralstrength values in acidic environment but remained abovethe ideal value. This result confirms that acidic environmentaffects mechanical properties of many restorative materials,including also flexural strength. Indeed, flexural strength isthe property that allows composites to resist chewing loads,so this property strongly affects the life of a restauration in theoral cavity [38].

Furthermore, the data collected in the present inves-tigation suggest that the percentage of the filler in thecomposites presumably does not affect flexural strength. Thisis in agreement with previous reports evaluating physicalproperties and depth of cure of composites [35, 39]. Flowablecomposites, such as flowable microfilled hybrid composite(Gradia Direct Flo, Group 8) and flowable bulk fill (SureFilSDR flow, Group 9), show a higher value of flexural strength

compared to supranano spherical hybrid composite (EsteliteAsteria, Group 7) and nanohybrid Ormocer based composite(Admira Fusion, Group 3). The latter present a higherpercentage of filler. In fact, some authors claimed that thereare other factors that can play a relevant role in modifyingthe flexural strength value such as stress transfer betweenfiller particles and matrix, as well as adhesion between thesecomponents [35, 39].

In the present report, also elastic modulus has beentested. Higher values were reported with nanofilled compos-ite (Filtek Supreme XTE, Group 1) and lowest values werereported with microfilled composite (Gradia Direct, Group4), flowable microfilled hybrid composite (Gradia Direct Flo,Group 8), and flowable bulk fill (SureFil SDR flow, Group9). As Filtek Supreme XTE (Group 1) showed the highestvalue of elastic modulus, this material can be consideredthe stiffest composite tested. The importance of the elasticmodulus ismainly related to the choice of the right compositefor a specific clinical situation: in fact, flowable composites areusually used in restorations of V class because their higherelasticity can absorb at best the chewing force in this specificregion of the tooth.On the other hand, in occlusal restoration,where the material resistance has to be maximized, stiffercomposites are more fit to the scope [38, 40]. Previousauthors evaluated elastic modulus of different compositematerials showing a significant increase of this variable afteroven postcuring [17]. No studies evaluated elastic modulusof composites after acidic immersion. In our study theimmersion in acidic drink did not affect elastic modulus of allmaterials tested, so no significant correlation between acidicenvironment and elastic modulus of composites was found.

Recent research showed a significant increase in elasticmodulus of various composite materials, with the increaseof filler content [41]. In fact, also in the present report somecomposites with higher filler percentages showed higherelastic modulus values, as flowable composites tested (groups8 and 9) showed significantly lower elastic modulus valuesthan higher filler composites (Groups 1 to 7). However, evenif the findings of the present report are promising, further invivo studies are needed in order to confirm the results.

5. Conclusions

The results of the present report, showed the following:(i) The various composite materials showed different

flexural strengths and elastic moduli. Higher values werereported with nanofilled composite (Filtek Supreme XTE).

(ii) Immersion in acidic drink lowered flexural strengthand elastic modulus of nanofilled composite (Filtek SupremeXTE). Other materials were not affected by acidic drinkimmersion.

Data Availability

Data are available upon request at andrea.scribante@unipv.it.

Conflicts of Interest

The authors declare that they have no conflicts of interest.

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Acknowledgments

Authors would like to thank the manufacturers for providingthe materials tested in the present report.

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